test_runner: add mockReturnValue and promise helpers

[araujogui]

Adds mockReturnValue(), mockResolvedValue() and mockRejectedValue() to MockFunctionContext as shorthands for common mockImplementation() patterns, matching the equivalent Jest/Vitest APIs.

fn.mock.mockReturnValue(42);
fn.mock.mockResolvedValue(42);
fn.mock.mockRejectedValue(new Error('boom'));

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.44%. Comparing base (7514ef8) to head (d659f36).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66631      +/-   ##
==========================================
- Coverage   92.79%   90.44%   -2.35%     
==========================================
  Files         422      791     +369     
  Lines      193669   276619   +82950     
  Branches    29886    53129   +23243     
==========================================
+ Hits       179712   250191   +70479     
- Misses      13630    16825    +3195     
- Partials      327     9603    +9276     

Files with missing lines	Coverage Δ
lib/internal/test_runner/mock/mock.js	97.38% <100.00%> (+0.50%)	⬆️

... and 499 files with indirect coverage changes

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